In cold pilger rolling a hollow billet is advanced in a rolling direction over a generally stationary mandrel while a pair of rolls squeeze the billet against the mandrel to form seamless pipe or tubing. The support or stand carrying these rolls is reciprocated through a short stroke in and against the rolling direction, often at high speeds up to 300 strokes/minute.
The common stand or support in which the rolls are journaled is reciprocated in the rolling direction by means of a crank drive. A tie rod has an outer end journaled on the reciprocal roll stand and an inner end eccentrically mounted on a crank arm or wheel that is continuously rotated at the desired stand reciprocation speed. Since the amount of throw is considerable, it is standard to provide counterweights to reduce vibration and strain on the machinery.
Thus, as described in U.S. Pat. No. 5,540,076 based on German 4,336,422 of Baensch and Bonsels, each of two crank arms connected to opposite sides of the roll stand carries a respective counterweight and a common drive motor is connected through respective identical gear trains to the cranks. This is a very large and complex mechanism that is very expensive to build and maintain, and that takes up a great deal of space.
German patent 962,062 of Zeunert employs a vertically effective counterweight. This system requires the base for the roll stand to be very expensively and massively built, as it must accept the vertically moving parts. A big below-ground area must be provided for the drive mechanism.
In German patent 3,613,036, U.S. Pat. Nos. 5,859,458, and 5,076,088 another system is described using planetary type crank drives for compensating out the forces in such a pilger rolling system. Such systems are highly effective, but only work with relatively small systems forming small-bore thin-wall tubing. The machinery becomes extremely large and unwieldy when applied to large rolling stands.
In all the known pilger cold-rolling systems there is the disadvantage that the throw-canceling systems are quite complex and expensive.